The inventor has found that in conventional electrical generation units of the type having a generator which must be excited or energised to produce an electrical energy output, as soon as a loading is applied to the output the electrical energy output drops. This problem is particularly acute in portable welding machines where the loading during welding is of such a nature that it can virtually shutdown the generator unless its drive means is substantially oversized.
According to a first aspect of the invention there is provided an electrical power generation unit including
drive means for driving a drive shaft;
a first electrical generator which is configured to be connected to and driven by the drive shaft in use;
a second electrical generator which is larger than the first generator and is configured to be connected to and driven by the drive shaft; and
the first generator being electrically connectable to the second generator such that, in use, substantially all the electrical energy generated by the first generator is used to excite or energise field coils of the second generator to permit electromechanical feedback regulation of output current from the second generator to smooth out fluctuations in the output energy delivered by the second generator under a loading condition; characterised in that the output voltage of the first generator is limited by the drive means to a voltage not exceeding the saturation voltage of the field coils of the second generator.
The second generator may be selected to be capable of supplying electrical power matching the power requirements of an electrical appliance to be energised.
The drive means may selected to be capable of supplying electrical power corresponding to the ratio of the maximum power characteristic of the second generator divided by the calibrated efficiency factor of the second generator.
A transmission ratio between the drive means and the second generator may be selected such that the output voltage of the second generator is limited by the drive means to a voltage approaching the saturation voltage of the second generator.
The first electrical generator may be a permanent magnet DC generator. The DC generator may be the DC motor of a vehicle cooling system fan, such as that provided on a Volkswagen (TM) utility vehicle.
Typically, the DC generator is mounted on a free end of the drive shaft. However, it may be mounted in any position and be driven by a belt and pulley system driven by the drive shaft.
The second electrical generator may be an AC alternator having field coils. Typically, the AC alternator is a standard 3-phase vehicle alternator.
The second generator may be connectable to the drive shaft by a belt and pulley system. The diameter of the pulley on the drive shaft may be selected so that, together with the operating characteristics of the primary and secondary generators, a desired output current at a specified voltage is provided from the secondary generator.
The electrical power generation unit may include a voltage regulator circuit connectable to a transformer on the output of the second generator for regulating the output voltage of the transformer at a predetermined voltage. Typically, the regulated output voltage is 220 V DC.
The electrical power generation unit may include a voltage rectifier circuit for rectifying the output voltage. The voltage rectifier may have a heat sink connectable in heat flow communication with the second generator for heat dissipation through a cooling system of the second generator. Typically the second generator cooling system includes a fan mounted to provide a flow of cooling air over the generator body.
The electrical power generation unit may include an output socket circuit connectable to permit electrical communication between any suitable tool and the power generation unit. Typically the output socket is a standard 3-pin type socket.
The electrical power generation unit may include a 3 phase rectifier and associated circuitry connectable to the power generation unit to form a welding unit having its own electrical power generation means. Typically, the alternator output is wired in delta configuration when used as a welding unit.
The power generation unit may include a battery charger circuit connectable to the power generation unit, for charging a battery connected to the battery charger or for boost starting an engine such as a vehicle engine when the battery usually employed for this purpose is inoperative.
The power generation unit may include a selector switch for selectively nominating between the circuits described above.
The electrical power generation unit may include a transportable mounting frame for facilitating the transportation of the unit. Typically, the mounting frame is a tubular cage having access openings for operator access to the power generation unit.
If required, the electrical power generation unit includes at least one additional secondary generator connectable to the drive shaft and the primary generator, in a similar fashion to that described above for the secondary generator, and co-operating with the other secondary generator in increasing the electrical energy output from the unit without the need for an increased size generator.
The drive means may be a fuel powered motor connectable to the drive shaft. The motor may be a petrol or diesel engine connectable to the drive shaft. The selection of petrol or diesel being an operational decision based on the surrounding circumstances such as fuel availability. In a specific embodiment the drive means may be an electric motor.
The invention extends to a transportable welding unit including a power generation unit as described above.
The invention further extends to a method of providing a substantially stable supply of electrical energy under loading conditions including the steps of:
connecting a first generator to a drive shaft of a drive means;
connecting a second generator to the drive shaft;
electrically connecting the first generator to the second generator such that, in use, substantially all the electrical energy generatable by the first generator is used to excite or energise field coils of the second generator; characterised in that the output voltage of the first generator is limited by the drive means to a voltage not exceeding the saturation voltage of the field coils of the second generator.
The second generator may be selected to be capable of supplying electrical power matching the power requirements of an electrical appliance to be energised.
The drive means may be selected to be capable of supplying electrical power corresponding to the ratio of the maximum power characteristic of the second generator divided by the calibrated efficiency factor of the second generator.
A transmission ratio between the drive means and the second generator may be selected such that the output voltage of the second generator is limited by the drive means to a voltage approaching the saturation voltage of the second generator.